In recent years, portable information terminals such as smartphones and tablet terminals have been widespread. Most of the portable information terminals are provided with active matrix display devices and input devices such as touch panels.
In an active matrix display device including light-emitting elements such as organic light-emitting diodes (OLEDs), variation in the threshold voltages of transistors that control the value of current supplied to the light-emitting elements in accordance with image signals (such transistors are also referred to as driving transistors) is likely to influence the luminance of the light-emitting elements. In order to prevent variation in the threshold voltage from influencing luminance of the light-emitting elements, Patent Document 1 discloses a display device which determines threshold voltage and mobility from a source voltage of a driving transistor and sets a program data signal based on the determined threshold voltage and mobility depending on a display image.
Many touch panels used in portable information terminals are capacitive touch panels. In a capacitive touch panel, a change in electrostatic capacitance which is caused when a finger of a user touches the touch panel is output as a current value. As a means for detecting the current value, a detection circuit with an operational amplifier is proposed (Non-Patent Document 1).